(1) Field of the Invention
This invention relates to a push button switch and, more specifically, to a push button switch suitable for use in a terminal machine of a computer or in an electric typewriter.
(2) Description of the Prior Art
General reference is made to the applicant's copending application U.S. Ser. No. 973,422 filed Dec. 26, 1978.
Generally speaking, push button switches of this kind has, as disclosed in U.S. Pat. No. 3,969,600, an inversion leaf spring made of a thin plate of beryllium copper or the like material disposed on a bottom surface in a horizontal plane. In operation, the inversion leaf spring is inversed as it is depressed vertically by a depression of a key top, thereby bringing a movable contact into contact with a fixed contact and turning the switch on. However, the push button switch of this kind has disadvantages such as a limited stroke of the keytop. In addition, the contact mechanism is so weak that it may be broken by a large depressing force applied to the key top.
In order to avoid the breakage of the contact mechanism, U.S. Pat. No. 3,773,998 discloses a push button switch using a coiled spring. However, this push button switch fails to provide sufficiently distinctive feel of actuation to the user of the switch.